Co-digestion with waste activated sludge for improved methanogenesis from high solids industrial waste

The objective of this work was to study the anaerobic digestion of an industrial waste with 84% total and 57% volatile solids content. The waste was also characterized by high total COD content, 42% by weight. The anaerobic digestion of the waste alone and its co-digestion with the waste activated sludge (WAS) that is generated at the industrial facility were investigated. Particularly, kinetics of digesting the waste alone and co-digesting it with the WAS were determined. The substrate utilization rates under varying initial substrate concentrations were determined in batch reactors by measuring the methane generation rates. Then the substrate utilization rates were modeled according to the Mound kinetics. The solution to nonlinear regression resulted in the maximum specific substrate utilization rates (k) of 0.138 and 0.165 g COD g VSS-1.day(-1) for the waste alone and the waste co-digested with the WAS, respectively. The half velocity constants (K-s) were 4.390 and 4.860 g COD l(-1) for the same conditions. It is important to note that since the methane generation data were used to determine the substrate utilization rates, these kinetic constants are likely to represent the methanogenic Archaea rather than the entire anaerobic consortium. It is concluded that the anaerobic co-digestion of this industrial waste with the WAS is beneficial from the digestion kinetics point of view since the k increased approximately 20% with the addition of the WAS. Moreover, there will be cost savings associated with digesting the WAS anaerobically rather than aerobically, the currently used method of WAS management, if anaerobic digestion is adopted in the future.